From roughly 1900 to 1950, the world of electronics was dominated by a now all but obsolete technology: vacuum tubes. These glass tubes were large, expensive and fragile and required a lot of current. In the 1940s, however, researchers made a technological breakthrough, which led to new components that were a quantum-leap improvement over vacuum tubes. These components are called semiconductors.

This chapter introduces you to the most basic kind of semiconductor, called a diode. Although diodes look a little like resistors (for details, check out Chapter 2 of this minibook), they behave very differently. Diodes have one ability that sets them apart: they let current flow freely in one direction, but block current if it tries to flow in the other direction. In other words, a diode is like a turnstile gate that you can walk through in one direction but not the other. This characteristic turns out to be incredibly ...

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